Austin and Max Leclaire are brothers. Austin is older, Max is younger. Like most siblings, they have many things in common and just as many that set them apart. For now, though, their strongest bond is over something they share — Duchenne muscular dystrophy (DMD), the most common lethal genetic disorder among children. Duchenne’s hallmark is increasing muscle weakness that eventually makes it hard to breathe and confines kids to wheelchairs, which is where Austin finds himself these days. Now 14, he lost the ability to walk four years ago, a development that helps explain why the disease looks so different in the two brothers today.

Because Max, 11, was still able to put one foot in front of another in the summer of 2011, he was eligible to enroll in a drug trial for Eteplirsen, which is designed for children like the Leclaire brothers who have trouble producing a protein called dystrophin. It’s likely that you’ve never heard of dystrophin, but it’s responsible for reinforcing and strengthening muscle fibers to gird them against wear and tear. Without it, normal activity strains the muscles, including the heart and lungs. Without it, kids with DMD die.

Eteplirsen helps affected children make small amounts of the protein, which moderates the breakdown of muscles so when the fibers contract, they’re not as damaged or inflamed. Eteplirsen doesn’t restore muscle so it can’t help a child like Austin walk again, but it does seem to slow, even stop, the progression of disease. That’s important since most kids with DMD don’t make it past their 25th birthday. It could be the reason that Max is still walking and Austin is not.

And that’s why their mom, Jenn McNary, 32, has added the title of “activist” to her already exhausting list of responsibilities. Austin and Max are just two of McNary’s kids; she has four others. They all need a mother advocating for them, but Austin needs her most of all.

It’s a cliché of parenthood that a mother would do anything for her child. McNary is trying. From her home in Saxtons River, Vt., a quaint village that spans half a square mile, she is taking on the U.S. Food and Drug Administration (FDA), petitioning them to apply a new federal law that reinforces the agency’s ability, in certain situations, to accelerate a drug’s approval. When the FDA, which approves pharmaceuticals, does agree to expedite temporary approval — it doesn’t do so often — the permanent green light ultimately follows, pending completion of years-long clinical trials.

A nod from the FDA would mean more patients, Austin included, could potentially take the drug. “I am telling them, Hey guys, here’s this drug, it fits that law,” says McNary. “Here are these kids who are on the drug and doing well. Here’s my son who’s not. I’m saying, Please make this drug available and give it accelerated approval.”

Preliminary trials have showed that Eteplirsen does what it’s designed to do with no adverse effects. Shouldn’t children who could benefit be able to access it before they get even weaker?

When companies study drug candidates in trials, they set strict criteria for which patients they test. In some cases, they’ll focus on the least affected patients because they might have the best chance of responding to a new treatment; more severely affected patients may be beyond help. Eteplirsen has not been studied in kids like Austin who can’t walk because focusing on those who can appears to be the speediest path to drug approval.

But Chris Garabedian, CEO of Sarepta Therapeutics, which makes Eteplirsen, believes the drug will help kids with DMD across the spectrum. If the drug were to receive temporary approval, doctors could prescribe to anyone they believe might benefit.“With a disease like Duchenne’s, where every year they have progressive muscle deterioration, waiting two or three additional years to just feel like we have a little more information doesn’t make sense,” says Garabedian. “These kids are dying.”

Garabedian recently requested a meeting with the FDA to make his company’s case that its drug is eligible to be considered for accelerated approval. He’ll share studies conducted both in the U.S. and in Europe. “Why do we subject families to waiting several more years to get confirmatory study results when there is early evidence that the drug works and it’s safe?” he says.

Eteplirsen is considered an orphan drug by the FDA, which means it treats a disease that affects fewer than 200,000 patients. With less than 15,000 children living with DMD in the U.S., Eteplirsen actually falls into an even rarer category: it’s called an “ultra orphan drug” because the mechanism by which it works will have an effect on less than 2,000 children with the disease.

Historically, the FDA has used its ability to accelerate approval sparingly. In 2011, just 10% of 30 new drugs qualified under the agency’s accelerated approval program; in 2012, only four made the cut. The agency is under heavy scrutiny to make sure that drugs are safe before they’re made widely available. The pressure may be even more intense when it comes to drugs for children, whose developing bodies are still developing. “There are special protections in place for children who participate in research,” wrote Sandy Walsh, team leader for medical products and tobacco in the FDA Office of Public Affairs, in an email response to questions about the process.

In July, Congress passed new legislation called the FDA Safety and Innovation Act; it included a new designation known as “breakthrough” therapy that joins three other programs to speed the development and availability of “potentially really beneficial” drugs, says Erica Jefferson, deputy director of the FDA Office of Public Affairs.

The new legislation is not very different from existing laws that allow for accelerated approval, which were applied to bring AIDS drugs to dying patients as quickly as possible. Accelerated approval grants a conditional thumbs-up contingent upon further studies. Since 1993, accelerated approvals have shaved an average of six to seven months off the traditional processing time.

“We don’t want to introduce anything that is not going to work and does more harm than good,” says Jefferson, who is prohibited from discussing the specifics of any drug under review. “But this is an acknowledgment that there are treatments out there that can be potential game-changers.”

The Leclaire boys, as do all kids with DMD, need nothing short of a game-changer. For Max, Eteplirsen has been just that. He’s regained 60% of normal dystrophin production, up from 0% when he began the trial in 2011 with 11 other kids. When he enrolled, he could walk but got so exhausted that he often collapsed into a wheelchair. But last year, he joined a soccer team. He now climbs stairs; in December he was able for the first time to join his class on a field trip to a nearby farm, ascending the steps on a regular schoolbus. “I don’t look at Max and think Duchenne’s any more,” says McNary. “His stamina is less than other kids and he gets more tired, but he really doesn’t have a whole lot of limitations.”

Austin, on the other hand, is failing. It’s excruciating to watch the divide between the two brothers widen. In October, Max marched in a Halloween parade, dressed as a skeleton. Austin was confined to his wheelchair, impersonating a hot dog cart. Max is growing in independence, able to twist or pop open his own food containers and carry a full-sized backpack to school. Meanwhile, Austin can barely pick up a glass of water. Max is running again, hiking up a sledding hill; Austin struggles to sit up. Austin can no longer put on his own jacket without help. He can’t roll over in bed on his own. With Max looking toward the future, his older brother can barely survive the present.

Austin was diagnosed a few months after Max was born. A late bloomer, Austin had trouble scooting up stairs; his pediatrician thought McNary was babying her first-born, carrying him too much. When Austin was 3, McNary took him to a physical therapist, who surmised that he had DMD. McNary was told not to worry; there was no way Max had it also. Then he was diagnosed too.

And so began a crash course in a disease McNary had never heard of. She can now spout off technical explanations about the exon, the segment of DNA that codes for a protein, that her boys are missing — exon 52. Eteplirsen helps compensate for its absence, hopscotching over the missing genetic material so that Max makes some dystrophin. McNary lays all this out in neat graphics on her website, DMDhero. “It’s not a cure,” says McNary, “but it’s enough.”

If it’s enough to make field trips and Halloween parades possible, that’s enough to motivate McNary to lobby the FDA to make the drug available to all children who could potentially benefit. McNary’s petition on Change.org asks the FDA director to “approve the medicine my boys need to survive — both my sons deserve to live.” She plans to present the document, which has garnered more than 170,000 signatures, on Feb. 13 in Washington, D.C., following meetings with members of Congress by hundreds of families who have children with DMD. Parent Project Muscular Dystrophy and the National Organization for Rare Disorders will be there too.

McNary hopes to meet with senior FDA officials. Should she get an audience, she’ll speak on behalf of all DMD parents when she conveys what it’s like to watch one son get better while the other gets worse: “We all know,” McNary will tell them, “that our kids are going to die if they don’t get something.”